1. Field of the Invention
The present invention relates to an image forming apparatus and image forming method, and more particularly, to technology for reducing relief effects by leveling the thickness of ink ejected as droplets onto a recording medium by an inkjet printer system using radiation-curable ink.
2. Description of the Related Art
An inkjet recording apparatus (inkjet printer) having an inkjet head (ink ejection head) in which a plurality of nozzles are arranged, is known as image forming apparatuses. An inkjet recording apparatus of this kind forms images by forming dots on a recording medium, by ejecting ink in the form of droplets from nozzles, while causing the inkjet head and the recording medium to move relatively to each other.
As inks used in inkjet printers, there are radiation-curable inks, which are cured by receiving radiation, such as ultraviolet (LV) light, an electron beam (EB), or the like. A radiation-curable ink includes, for example, a coloring material, a polymerizing monomer or oligomer, a polymerization initiator and a polymerization promoter which promote a bridging reaction or polymerization reaction of the monomer or oligomer with a photocatalytic reaction, and the like. Therefore, when irradiated with radiation, the radiation-curable ink hardens due to the bridging reaction or polymerization reaction.
In an inkjet printer system that uses a radiation-curable ink of this kind, usually, all of the solvent component is cured. Thus, the print regions on the recording medium stand out in a projecting shape and become fixed onto the recording medium while creating relief effects (step difference) on the printed object. This can be problematic, depending on the intended use of the printed object.
On the other hand, it is known that the thickness of ink droplets deposited on a recording medium by an inkjet recording apparatus using radiation-curable ink can be adjusted in such a manner that desirable print quality and storage properties are obtained (see, for example, Japanese Patent Application Publication No. 2003-136697).
This technique relates to a recording apparatus which combines an inkjet recording apparatus using radiation-curable ink for recording variable information and an image forming apparatus based on another system for recording non-variable information. As a method for adjusting the thickness of the ink droplets deposited by the inkjet recording apparatus, the technique adopts ink thickness control by means of polishing, pressurization, heating, or an auxiliary light exposure device.
However, there is a possibility that the recording apparatus according to Japanese Patent Application Publication No. 2003-136697 has the following problems. More specifically, the applicable image recording apparatus is limited to being the recording apparatus that includes an inkjet recording apparatus and an image forming apparatus based on another system.
Moreover, if the method for adjusting the thickness of the ink droplets deposited by the inkjet recording apparatus is based on polishing, then there is a possibility of reducing print density due to removal of necessary coloring material, and there is also a possibility that the image is soiled by the occurrence of powder caused by the polishing.
Further, if the thickness of the ink droplets is adjusted by pressurization, then the dot diameter and the line width of ink, and the like, can expand, and this leads to a decline in density and resolution. Furthermore, if the thickness of the ink droplets is adjusted by heating, then the diameter and the line width of the ink droplets, and the like, can expand, and this leads to a decline in density and resolution.
Furthermore, the method for adjusting the thickness of the ink droplets by means of an auxiliary exposure device increases the thickness of the ink, in order to match the thickness of a non-variable information section. Therefore, it cannot be used with the object of leveling the ink droplets and removing projecting shapes therein by reducing the thickness of the ink.